1. Field of Invention
The field of the currently claimed embodiments of this invention relates to inorganic solutions and solution processes for producing electronic and/or electro-optic devices and devices made by the solutions and processes.
2. Discussion of Related Art
Due to the general concern over global warming, and increasing demand for energy, much research has focused on developing a feasible method for renewable energy generation. Among renewable energy sources, solar energy has attracted the most attention due to the direct conversion of energy to electricity from the sun. However, the scaling up of production and the reduction of cost are still the main issues for photovoltaic technologies to compete with traditionally generated power (Contreras, M. A., Ramanathan, K., AbuShama, J., Hasoon, F., Young, D. L., Egaas, B., & Noufi, R., Prog. Photovolt: Res. Appl. 13 209-216 (2005)). Many research efforts have shifted to so-called “second generation” solar cells, which employ compound semiconductors and are based on a single p-n heterojunction (Mitzi, D. B., Kosbar, L. L., Murray, C. E., Copel M., & Afzali, A., Nature 428 299-303 (2004)). Due to the suitable band gaps, and high absorption coefficients, Cu(In,Ga)Se2 (CIGS) and its related materials have been the most attractive absorber materials for the fabrication of low-cost, high-efficiency solar cells. However, with rising concerns regarding the supply of the rare metal indium in the mass production stage, low cost, environmental harmless Cu2ZnSn(S,Se)4 (CZTSSe)-based thin film photovoltaics using earth abundant materials have been expected to provide a potential alternative.
Typically, the absorber layers of thin film solar cells are deposited by either evaporation or sputtering techniques that requires a vacuum environment. Those vacuum-based techniques need to overcome not only complicated processes and non-uniform film composition, but also a large capital investment is required in order to move thin film solar cells into commercialization. Many researchers have focused on reducing production cost through solution-processable active layers. However, most of the attention has been devoted to organic semiconductors. Despite numerous advancements in this area, organic semiconductors still have problems with stability in air. Recently, Mitzi et al. have reported a method for solution processing of inorganic materials with mobilities around 10 cm2 V−1 s−1, which is comparable to materials produced through traditional processing (Mitzi, D. B., Kosbar, L. L., Murray, C. E., Copel M., & Afzali, A., Nature 428 299-303 (2004); Milliron, D. J., Mitzi, D. B., Copel, M. & Murray, C. E., Chem. Mater. 18 587-590 (2006); Milliron, D. J., Mitzi, D. B., U.S. Patent Application 0158909 A1 (2005)). However, according to their approach, zinc or zinc chalcogenide cannot be dissolved into their hydrazine solutions. In their process, zinc or zinc chalcogenide constituent suspends as nanoparticles in the precursor solution. Therefore, there remains a need for improved solutions and solution processes for producing electronic and electro-optic devices.